1. Field of the Invention
The present invention relates to a so-called "high temperature" nozzle and particularly to a plasma nozzle whose inner profile is specifically designed to allow the plane board type testing of specimens, particularly of materials that must withstand high thermal and pressure stresses.
The invention particularly concerns the testing of materials intended to form the hot parts of space missiles bound to meet heavy conditions of atmospheric reentry that result in high temperatures (from 110020 to 1900.degree. C.) and low pressures for a comparatively long time (about half an hour).
2. Discussion of Background Information
The so-called "plane board" type of tests consists in placing a specimen made up of a monolithic block or of several elements of one or several materials to be tested, parallel to a nozzle jet, and in measuring the static pressure as well as the temperature at various points of the surface of the specimen or of the assembly of materials for surface incidences in relation to the nozzle jet ranging from 0 to a few degrees.
Such tests are carried by means of an arrangement comprising a plasma generator that produces a high temperature flow, a nozzle placed downstream from the generator and transforming the flow so as to adjust it to the required testing conditions, a testing chamber into which the nozzle opens and wherein the arrangements for displaying the specimens or similar are installed as well as the various measuring means necessary for testing, a diffuser located downstream from the chamber and meant to collect the flow after it has run onto the specimens, a heat exchanger so as to cool the flow, and a vacuum system placed downstream intended to maintain, inside the chamber, the low pressure level required for that type of tests.
The specific shape of the specimens for "plane board" testing requires a nozzle with an appropriate design consisting of a rectilinear edge on the downstream end liable to be connected to one of the rectilinear edges of the specimen.
Two types of nozzle are currently used for "plane board" testing, namely a so-called "square tube" nozzle and a "semicircular" nozzle.
The "square tube" nozzle comprises a divergent whose section, at the outlet, is slightly rectangular with round-off angles, whereas the "semicircular" nozzle is an axisymmetric nozzle whose divergent is reduced to half according to a plane comprising the axis of the nozzle.
The tests that are carried out with those types of nozzle are not fully satisfactory since the nozzles generate a very disturbed whirling stream, at the outlet, the stream being incompatible with the very homogeneous hot gas flow required during "plane board" testing, so as to obtain a distribution of the static pressures and of the thermal flows as uniform as possible on the exposed surface of the specimen.